FIG. 43 is a block diagram of a conventional switch duplexer. A circuit configuration of an antenna switch duplexer in a composite terminal of a system called a 900-MHz-band GSM which is a cellular phone system serving in Europe and a system called a 1.8-GHz-band DCS will be explained as an example.
In FIG. 43, reference symbols 1001 to 1005 denote input/output ports, 1006 and 1007 denote control terminals, 1008 to 1011 denote diodes, 1012 and 1013 denote transmission lines, 1014 and 1015 denote bandpass filters, and 1016 denotes a diplexer. Diplexer 1016 is generally configured by a circuit obtained by combining low-pass filter 1016a and high-pass filter 1016b. Reference symbol HPF denotes a high-pass filter, LPF denotes a low-pass filter, and BPF denotes a bandpass filter.
An antenna (not shown) is connected to input/output port 1005. A signal caught by the antenna is distributed into a GSM-band signal and a DCS-band signal by diplexer 1016 first. Transmission lines 1012 and 1013 are set to ¼ of wavelengths in a GSM band and a DSC band. When a positive voltage is applied to control terminal 1006 to cause a current to flow, diodes 1008 and 1010 are turned on, and input/output ports 1005 and input/output port 1001 are connected to each other. Similarly, when a positive voltage is applied to control terminal 1007 to cause a current to flow, diodes 1009 and 1011 are turned on, and input/output port 1005 and input/output port 1003 are connected to each other. When no voltage is applied to control terminals 1006 and 1007, diodes 1008 to 1011 are turned off, input/output port 1005 and input/output ports 1002 and 1004 are connected to each other consequently.
In general, input/output ports 1001 and 1003 serve as ports for transmission, bandpass filters 1014 and 1015 serve as filters for limiting a reception band, and input/output ports 1002 and 1004 are used as input/output ports for reception. As prior art document information related to the invention of the application, for example, Patent Document 1 is known.
In the conventional switch duplexer, since diplexer 1016 is constituted by a circuit obtained by combining low-pass filter 1016a and high-pass filter 1016b, although diplexer 1016 can separate signals in different frequency bands from each other, diplexer 1016 cannot separate two signals each having the same frequency from each other. Since the switch duplexer constituted by control terminals 1006 and 1007, diodes 1008 to 1011, and transmission lines 1012 and 1013 can temporally select an input/output port connected to diplexer 1016 depending on the states of diodes 1008 to 1011, two signals each having the same frequency can be used while being temporally switched. However, a problem in which the two signals each having the same frequency cannot be transmitted or received at the same time is posed. This, for example, in a cellular phone system, makes a data transmission/reception speed low.    [Patent Document 1] International Publication No. 01/045285 booklet